Designing an RF transceiver

[William Dillon] is finishing up his degree. His final project as a student was to design an RF transceiver. He decided to work with the Microchip MRF49XA, which runs around $3 but will cost you $20 if you want it in a ready-to-use module. He didn’t find a lot of info on the Internet about communicating with these chips so he’s shared his design, code, and board files. If you’re ever wanted to delve into RF design this is a good primer. [William] talks about building around the example circuit from the datasheet but also includes a discussion of the calculations he made in working with the 434 MHz band, and an AVR-based library for using his module.

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15 thoughts on “Designing an RF transceiver”

The MRF49XA is used in the Radica Puppy Tweets toy. You get two of these MRF49XA modules, one integrated into a USB dongle. I haven’t yet got to hacking these myself, so I have no idea how easy it is to hack these, but it can’t be rocket science. Go to the FCC OET license site (https://fjallfoss.fcc.gov/oetcf/eas/reports/GenericSearch.cfm) and look up FCC IDs “PIY T7004D1″ and “PIY T7004T1″. In the details, there’s even full circuit diagrams!

Great find. There are several neat things about this. The first is that the design company is obviously using Altium schematic capture. The second is that they either use, or thought they may want to use, the direct interface to the frequency-shift-keying (FSK) pins. These are FSK and DCLK. This is an option if you want to use a higher bit rate, or if you want more control over packet synchronization. If you wanted to integrate this into your own project, you’d need to customize the schematic on my design for the 915 Mhz balun, and some changes to the code. Also, you’d need to figure out what bitrate and packet structure they’re using.

There’s a lot that can be done with quantity and the magic of outsourced labor. I added up the parts alone in single (or 10 for passives) unit quantities from Digikey and it came out to $5.73 w/o the PCB. Keep in mind that they also don’t use a package for the IC, opting instead for the cheaper epoxy blob.

It’s very interesting to me, however, that the datasheet doesn’t give really any information about how to use it. When you find the programming guide, it’s obvious that this is likely made from the same IC. If that is the case, the library should be useful for those as well. There is some precedent for this, SILabs has a chip that is identical: http://www.silabs.com/products/wireless/EZRadio/Pages/Si442021.aspx

I am attempting to develop code for two RF transceivers to transmit data through a PIC16F877A micrcontroller. I am a first time user of both and not very familiar with programming in general. Can anyone offer some advice/assistance?

Is it possible to make a tranciever device so I can take over power someone’s satellite TV signal, like overpower their signal going to their dish and transmit mine to their TV, so I wouldn’t have to hardwire anything?